Polyfluorinated alcohols of the type R.sub.F CH.sub.2 CH.sub.2 OH, wherein R.sub.F denotes a perfluoroalkyl radical, are precursors of treatment agents for surfaces and materials. These compounds can be prepared starting with 1-iodo-2-perfluoroalkyl-ethanes, R.sub.F C.sub.2 H.sub.4 I following different methods; for example, reacting with an aqueous solution of an amide (publication JP 72-37,520) reacting with fuming sulfuric acid (U.S. Pat. No. 3,283,012), or forming, in tributyl phosphate, an organozinc intermediate which is subsequently, oxidized, and then hydrolyzed (French Patent 2,521,987). However, the synthesis of these alcohols by the electrochemical reduction of R.sub.F C.sub.2 H.sub.4 I compounds has not yet been accomplished.
The preparation of perfluoroalkanecarboxylic acids R.sub.F COOH or perfluoroalkanesulphonic acids R.sub.F SO.sub.3 H has formed the subject of many investigations, because of the utility of these acids as precursors of surface active agents. Their synthesis was first carried out starting with the acid chlorides of alkanecarboxylic acids and alkanesulphonic acids respectively, by electro-fluorination in anhydrous hydrofluoric acid (U.S. Pat. No. 2,519,983). However, this technique which is well-suited to the preparation of acids of low molar weights, gives very low yields in the preparation of acids of high molecular weights. In order to overcome this drawback, Calas et al. (J. Electroanal. Chem., 1978, 89, 363-372) have proposed the electrochemical reduction of perfluoroalkyl iodides R.sub.F I on a polarized mercury bed in the presence of SO.sub.2 or CO.sub.2, which makes it possible to prepare perfluoroalkanesulfonic or perfluoroalkanecarboxylic acids with 70% and 90% yields respectively. Unfortunately, the use of mercury makes the application of this method on an industrial scale prohibitory.